Abstract—Metallographic method investigated the process of convergence of thick-walled cylindrical copper shells under the action of an explosion. The explosion was initiated from eight points evenly spaced in a circle on the surface of the explosive surrounding the shell. At the intermediate stage of convergence, eight outliers formed on the inner surface of the shell. The convergence of the shells into the cylinder is completed by expanding and closing the emissions. The formation of outliers is explained by the occurrence of plastic (cumulative) jets at the deformation front. Jets occur when adjacent deformation projections collide. Areas of localized deformation were found inside and around the ejections, which is associated with this method of initiating an explosion. It is established that high-speed deformation of copper during the convergence of shells is accompanied by the formation of a large number of twins. There are more twins in the outer zones of the shells than in the inner ones.

The process of convergence of copper thick-walled cylindrical shells under the action of an explosion is studied using the metallographic method. The explosion was initiated at eight points evenly spaced around a circle on the surface of the explosive surrounding the shell. At the intermediate stage of convergence, eight ejections were formed on the inner surface of the shell. The convergence of the shells into a cylinder is completed due to the expansion and closure of ejections. The formation of ejections is explained by the rise of plastic (cumulative) jets at the deformation front. Jets arise when adjacent deformation protrusions collide. Regions of localized deformation were detected in and around the ejections, which is associated with the method of initiating the explosion. It has been established that high-strain-rate deformation of copper during the convergence of shells is accompanied by the formation of a large number of twins. In the outer zones of the shells, there are more twins than in the inner ones.

Abstract—It has been found that austenitic stainless steel produced by selective laser melting undergoes successive recovery, polygonization, and recrystallization as the heating temperature increases, similarly to deformed steel. The temperatures of structural transformations are lower than those after deformation. An unusual chessboard-type structure was discovered during heating to 650–700°C (in the temperature range of incomplete recrystallization). Such structure develops as the intersection of mutually perpendicular bands of small recrystallized grains.

The high-rate convergence of copper cylindrical shells with a diameter of 48 mm and a wall thickness of 4 mm is studied at various intensities of explosive loading. Two structural mechanisms of the loss of stability of the radial deformation front are described. A diagram of structural changes reflecting the successive stages of the convergence process is presented. An interrelation is found between the number of protrusions on the shell surfaces during their corrugation at the intensity of explosive loading. It was found that high-rate longitudinal deformation during convergence has a pulsating character. It was found that the temperature rises to ~500°С in the center of the converged shell and that it can be higher than 1000°С at a high rate of spall-pore collapse.

The microstructure and mechanical properties of chromium–nickel austenitic stainless steel fabricated by selective laser melting using a Realizer SLM100 3D printer have been investigated in this work. The structure of the studied specimens has been formed by the complete melting of the initial powder and high-speed cooling of the melt. Cooling of the melt initially leads to the formation of δ ferrite, and then, polymorphic δ → γ transformation results in the formation of the final austenitic structure. The structure of δ ferrite which formed during melt crystallization has been found to exhibit a clear pattern of periodicity. The periodicity depends on the parameters of the melting process, such as the distance between neighboring bands formed during laser-beam traveling (intertrack distance) and the step of platform feeding (distance between layers). The polymorphic δ → γ transformation takes place by a disordered mechanism and no austenite texture forms. However, some structural heredity remains. It can be seen in the orientational relationship between some austenite grains and δ-ferrite grains. The steel fabricated by laser melting is shown to have high mechanical properties such as the yield strength, the ultimate tensile strength, and the tensile elongation at a strain rate of 10 –2 s –1 , which are 320, 765 MPa, and 50%, respectively. The yield strength and ultimate tensile strength of the specimens under dynamic compression by the Hopkinson–Kolskii technique at an average strain rate of 10 3 s –1 are 550 and 945 MPa, respectively.

The deformation structure in copper that forms upon the convergence of a massive cylindrical shell into a cylinder is studied in this work. The shell in the deformation zone was subjected to high-speed deformation (~10 4 1/s) with large values of true strain ( e varied from 0.8 to 2.0). It is shown that two types of structures were formed under deformation: regions containing disperse grains with high-angle boundaries and twins and regions with deformation cells having low-angle boundaries. It is found that the twins that arose at the early stages of deformation are distorted upon further deformation: their rectilinear boundaries are bent, the orientation relationships with the matrix are violated, and high-angle boundaries of arbitrary orientation are formed.

An experiment is performed for explosive convergence (collapse) of a cylindrical shell of low carbon steel with a ferrite-perlite structure. It is revealed that during ultra-rapid heating caused by high-speed deformation austenite formation occurs in an unusual sequence: first, free ferrite is converted, then pearlite. The decrease in free ferrite transformation temperature is explained by action of high pressure, as well as by varying degrees of heating steel structural constituents. An effect of barothermal quenching is observed, as a result of which a pearlite-martensite structure forms.

The recrystallization process in copper subjected to high-rate compression deformation by collapsing a massive cylindrical shell into a cylinder has been studied in this work. Recrystallization occurs in two stages due to the peculiarities of the deformation structure. At the first low-temperature stage, regions with deformation-induced highly-misoriented (over 15 degrees) grains are recrystallized. At the second stage, regions containing deformation-induced cells with low angular boundaries are recrystallized. Recrystallization in copper after loading with a plane shock wave is investigated for comparison. The recrystallization occurs via migration of grain boundaries to form one step.

The structural mechanisms of buckling and the deformation behavior of copper and steel cylindrical shells (pipes) during collapse under the action of an explosion are studied. The dependence of deformation behavior on the transverse dimensions of the shell and properties of the loaded material is described. It is established that the stability of radial collapse depends on absolute dimensions of the shell rather than relative dimensions, with the collapse of large-diameter shells occurring more stably. It is demonstrated that the collapse stability is violated due to the formation of a characteristic pattern of localized strain in the sample, consisting of homogeneous, orderly arranged structural elements whose dimension depends little on the material properties and experimental conditions. A criterion for stable radial collapse that relates the characteristic dimensions of the structural element of localized strain and the shell radius is proposed.

Metallography has been used in this study to investigate copper samples cut from cylindrical shells collapsed under shock wave loading. Spallation phenomena (either the shell is divided into concentric rings, or a wide zone with spallation cavities and cracks is formed), which occur in shells under shock wave loading are considered. High-rate deformation during inertial convergence heals pores and cracks. Traces of healing remain in the microstructure. Various cases of nonradial convergence, when a stable circular deformation front is lost, are observed. Bends appear on the thin-walled shell and the shell crumples during its converging. Periodically arranged protrusions form on the inner surface of the thick-walled shells. They subsequently join together, converging to the center of the shell. A wave-shaped relief, protrusions, dents, and corrugation on the outer surface indicate the loss of stability.

The paper studies the decomposition of a supersaturated solid solution with a precipitate of particles of the copper-zirconium phase in the Cu-0.06 wt.%Zr and Cu-0.21 wt.% Cr-0.20 wt.%Zr alloys in two initial states, i.e. after solid-solution quenching and after high strain rate deformation (10(5) s(-1)) by the method of dynamic channel-angular pressing (DCAP). It has been shown that the decomposition of the supersaturated solid-solution of zirconium in copper in the quenched micro-alloyed Cu-Zr and low-alloyed Cu-Cr-Zr alloys occurs in two stages. At the first stage, nanoparticles of a metastable copper-zirconium phase are formed. The crystal structure of the nanoparticles is close to the structure of the copper matrix. At the second stage, particles of the equilibrium Cu5Zr phase are formed in the form of rods. Annealing (aging) of the alloys deformed by DCAP is characterized by the predominance of heterogeneous precipitation of Cu5Zr nanoparticles at sub-grain boundaries and dislocations, and the decomposition begins at a lower temperature. The particle size is less by an order of magnitude than that in the quenched state. The precipitation of nanoparticles at dislocations retards the formation of recrystallization centers. It has been shown that the treatment including DCAP and annealing at 450 degrees C for 1 h substantially increases microhardness of the micro-alloyed Cu-0.06%Zr alloy by a factor of 2.7 as compared to the initial quenched state. This behavior is related to substantial structure refinement during DCAP and decomposition of the supersaturated alpha-solid solution of copper.

The collapse of copper and steel shells (pipes) into solid cylinders under the action of explosion is investigated.The phase and structural transformations occurring in materials affected by high-speed deformation during collapsing are studied; fracture phenomena associated with the release of a shock wave onto the free inner surface of the shell are investigated.It is shown that the convergence of shells of large diameter proceeds more steadily; it is established that the stability of convergence depends on the absolute dimensions of the shell rather than on the relative ones.It is shown that comparing the results of experiments on collapsing shells from various materials makes it possible to recreate partially the loading conditions that were not recorded directly in the experiment, in particular, to calculate the mass velocity of the shell and the pressure in the front of the shock wave.

The microstructure, mechanical and functional properties, including electrical and wear resistances have been investigated for the Cu-0.09%Cr-0.08%Zr and Cu-0.14%Cr-0.04%Zr alloys subjected to high-speed dynamic channel angular pressing (DCAP) followed by annealing (aging). It was shown that DCAP led to the formation of a submicrocrystalline (SMC) structure (d = 200–400 nm) with second-phase precipitates up to 5 nm in a size. The sequence of decomposition of a copper based α solid solution, accompanied by recrystallization and precipitation of second-phase nanoparticles during annealing (aging), was determined. DCAP and aging at 400-450 °C led to a decrease in the electrical resistance of the Cu-Cr-Zr alloys from 4.2 to 2.1 µΩ·cm and to a drastic increase in their strength properties (σu from 197 to 542 MPa, σ0.2 from 94 to 464 MPa), while retaining reasonable ductility. It was revealed that the SMC structure processed by DCAP and annealing (aging) at 400 °C can be additionally strengthened after sliding friction tests due to the formation of a nanocrystalline structure in the surface layer.